/*-
 *  * Copyright 2016 Skymind, Inc.
 *  *
 *  *    Licensed under the Apache License, Version 2.0 (the "License");
 *  *    you may not use this file except in compliance with the License.
 *  *    You may obtain a copy of the License at
 *  *
 *  *        http://www.apache.org/licenses/LICENSE-2.0
 *  *
 *  *    Unless required by applicable law or agreed to in writing, software
 *  *    distributed under the License is distributed on an "AS IS" BASIS,
 *  *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  *    See the License for the specific language governing permissions and
 *  *    limitations under the License.
 */

package org.datavec.api.util.files;

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

/**
 * A very simple iterator over a list, that takes an optional int[] for the order.
 * If the order array is not present, elements are returned in sequential order.
 *
 * @author Alex Black
 */
public class ShuffledListIterator<T> implements Iterator<T> {

    private final List<T> list;
    private final int[] order;
    private int currentPosition = 0;

    public ShuffledListIterator(List<T> list, int[] order) {
        if (order != null && list.size() != order.length) {
            throw new IllegalArgumentException("Order array and list sizes differ");
        }
        this.list = list;
        this.order = order;
    }

    @Override
    public boolean hasNext() {
        return currentPosition < list.size();
    }

    @Override
    public T next() {
        if (!hasNext()) {
            throw new NoSuchElementException();
        }

        int nextPos = (order != null ? order[currentPosition] : currentPosition);
        currentPosition++;
        return list.get(nextPos);
    }

    @Override
    public void remove() {
        throw new UnsupportedOperationException("Not supported");
    }
}
